Field of the Invention
The present invention relates generally to BOP piston booster assemblies for shear rams and, more particularly, to a BOP booster piston assembly mounted between hydraulic actuators in bonnet end caps that contain hydraulic pistons used to open the rams to change out the shear members.
Background of the Invention
Blowout Preventers (“BOP”) are frequently utilized in oilfield wellbore for pressure control involving shearing tubulars and closing off a wellbore. A BOP, or a BOP stack, may include a first set of rams for sealing off the wellbore and a second set of shear rams for cutting pipe such as tubing, wireline and/or intervention tools. Many different sets of rams may be utilized. BOP stacks can be quite bulky and heavy expensive. With increasing size, BOP stacks typically become much more expensive for initial cost as well as for installation and removal.
Shear ram BOPs may frequently require maintenance after cutting pipe. In order to open the BOPs to change the shear members, hydraulic actuators located within bonnet end caps may be utilized.
BOPs utilize hydraulic pistons, referred to herein as operating pistons, to operate the rams, including the rams that utilize shearing members. The operating pistons for the BOP are often mounted between the bonnet end caps that contain hydraulic pistons utilized to open the bonnets for access to the shearing members. For this reason, the diameter of the hydraulic pistons utilized to operate the shearing pistons for these types of BOPs is limited.
To cut larger pipe than can be cut by the operating pistons utilizing the maximum or optimum practical hydraulic fluid pressure, booster piston assemblies have been utilized in the past that are utilized in addition to the operating pistons. However, when the operating pistons are positioned between the bonnet end caps, and the booster pistons are mounted axially thereto, the booster piston assemblies have been limited in size due to the bonnet end caps. Accordingly, these types of prior art booster piston assemblies are also limited in diameter, which in turn limits the amount of force that can be produced by the booster pistons.
Further, the addition of booster piston assemblies on either side of the BOP results in the need to add hydraulic lines that may be exposed to damage due to moving elements that may hit the BOPs and damage the hydraulic lines (e.g. items being lifted).
The following patents discuss background art related to the above discussed subject matter including examples of prior art booster piston assemblies:
U.S. Pat. No. 6,244,560, issued Jun. 12, 2001, to Chris Johnson, discloses a ram actuating mechanism for a blowout preventer, the ram actuating mechanism including a hydraulic booster for enhancing the ram closing force. The ram actuating mechanism may be compatible for use with primary pistons which include internal moving components, such as self locking pistons. The ram actuating mechanism provides a hydraulic booster without increasing the diameter of the booster pistons above the diameter of the primary piston, such that BOP stack height need not be increased to accommodate a relatively large diameter hydraulic booster. The ram actuating mechanism may utilize the same piston housing as used by the primary piston, and the booster pistons may act mechanically in series upon the primary piston to increase axial ram closing force. The ram actuating mechanism may be capable of retro-fitting to existing ram actuating mechanisms.
U.S. Pat. No. 5,178,360, issued Jan. 12, 1993, to Terry Young, discloses a valve actuator or a booster module for an existing valve actuator that provides an incremental force to the valve stem at a position close to valve closure. The force is stored in a spring which is held in the compressed position by a collet. Upon sufficient movement of the valve actuator stem in the direction towards valve closure, the collet which had previously held the spring in a compressed position is freed to move to allow the spring to expand against the collet. Since movement of the collet has caused it to be engaged to the valve actuator stem, the spring forces are transmitted directly to the valve actuator stem via the collet. The spring is oriented in a direction substantially parallel to the valve stem so that substantially all of its retained energy is transmitted directly to the valve stem through the collet.
U.S. Pat. No. 5,205,200, issued Apr. 27, 1993, to John J. Wright, discloses a linear actuator used in moving, for example, gate valves, sluice gates and the like, wherein an increased thrust is required during initial movement. The present invention includes, as part of the linear actuator, a booster piston movably disposed about a piston rod; further included on the booster piston is a thrust column disposed radially between the booster piston and the piston rod so as to define an annular fluid channel for enabling fluid to move upwardly so as to contribute a substantial additional thrust component to move the primary piston.
U.S. Pat. No. 6,969,042, issued Nov. 29, 2005, to Stephen Gaydos, discloses a blowout preventer with a main body; a base releasably connected to the main body, the base having a base space therein, the base having a ram shaft opening; a primary piston movably disposed within the base space; a ram shaft to which the primary piston is connected, the ram shaft including a ram end and a piston end; a ram connected to the ram end of the ram shaft; a housing connected to the base, the housing having a housing space therein, the housing including a middle member with a member opening; a booster piston movably disposed within the housing space and having a booster shaft projecting therefrom and a booster shaft space therein; the shaft including a push portion selectively movable to abut the ram shaft to prevent movement of the ram shaft and to transfer force of the booster piston to the primary piston; and power fluid apparatus for the primary piston and the booster piston.
U.S. Pat. No. 7,374,146, issued May 20, 2008, to Whitby et al., discloses a hydraulic blowout preventer operator comprises a first piston rod coupled to a closure member. The operator further comprises a first operator housing coupled to a bonnet and a head. The first piston rod extends through the bonnet into the first operator housing where is couples to a first piston disposed within the first operator housing. The operator further comprises a second piston rod coupled to the closure member. The second piston rod has a longitudinal axis that is parallel to a longitudinal axis of the first piston rod. The second piston rod extends through the bonnet into a second operator housing and is coupled to a second piston that is disposed within the second operator housing.
Chinese Patent No. CN 201865613, issued Jun. 15, 2011, to Shanghai SK Petroleum & Chemical Equipment Corporation Ltd., discloses a combined oil cylinder for a ram preventer with a shearing function. The combined oil cylinder comprises a side door, a ram control hydraulic cylinder assembly, a shearing boosting hydraulic cylinder assembly and a hydraulic cylinder cover which are sequentially connected and installed. The ram control hydraulic cylinder assembly comprises a ram control hydraulic cylinder, a ram control piston and a ram control piston rod. The shearing boosting hydraulic cylinder assembly comprises a boosting hydraulic cylinder, a boosting piston and a boosting piston rod. The combined oil cylinder for the ram preventer with the shearing function provided by the present utility model ensures that the size and the weight of the ram preventer of a hinge switch side door are not increased, can simultaneously effectively increase the pushing force of the piston rod to shear a tube string in a well.
The above prior art does not disclose a booster piston assembly as described in the present specification. Consequently, those skilled in the art will appreciate the present invention that addresses the above and/or other problems.